The present invention relates to an image read-out method and apparatus for reading a half-tone image with a storage-type image sensor (hereinafter referred to simply as an image sensor), and more particularly to a method and apparatus suitable for reading a color image.
In general, an image readout apparatus is used as an input unit for an image reproducing apparatus or an image recording apparatus. An image readout apparatus is also used for sampling the characteristics of an image. For example, prior to color printing with a color printer, three-color (blue, green, red) densities of a plurality of points defined on a color original (color negative film, color positive film or the like) are measured. Color originals are scene-classified based on the three-color density of each point. Each classified scene is then subjected to color correction to reproduce a fine, color-balanced print.
Conventionally, a known image readout apparatus is constructed of: three image sensors, each photoelectrically converting a corresponding one of three colors of light into an electric signal and storing it; three signal processors for processing time-sequential signals outputted from the respective image sensors; and a storage unit for storing the outputs of the signal processors. The signal processor of the image readout apparatus of this type is provided independently for each color and is expensive due to its high speed operation for picking up the respective time sequential signals in parallel. Therefore, there is a problem that the apparatus is complicated and expensive.